- Email: [email protected]
Absolute-dated, high-resolution records of water balance changes during the last glacial period and deglaciation from lacustrine cave deposits in the Bonneville Basin, Utah, USA
Abstracts / Quaternary International 279-280 (2012) 233–345
HIGH RESOLUTION PALAEOCLIMATE LAKE AND PEAT RECORDS FROM FUEGO-PATAGONIA FROM THE LGM TO THE EARLY-HOLOCENE Robert McCulloch. University of Stirling, United Kingdom E-mail address: [email protected]
The southern Andes lie athwart the zone of westerly precipitation which sustains the maritime Patagonian ice fields. During the Last Glacial Maximum (LGM) the southern Andean ice fields formed a single coterminous ice cap, some 200 km wide and over 1,800 km long. Climate records from Fuego-Patagonia spanning the LGM and deglaciation are few. Palaeoclimate change has to date been inferred largely from reconstructions of glacial fluctuations of the outlet glaciers draining the ice fields. We present two high resolution palaeoecological records dated to 30.3 ka and 22.8 ka supported by sedimentological and geochemical proxies from Lago Pato, Torres del Paine (51oS) and Punta Yartou (53oS), Tierra del Fuego, southern Patagonia. Robust age-depth models are provided by 14C dating and tephra layers. These two records lie close to the present southern Beech forest / steppe zone of transition and provide sensitive records of shifts in these ecotonal boundaries in response to climatic variations. A synthesis of the two records demonstrates the early deglaciation of FuegoPatagonia following the LGM but the persistence of tundra vegetation indicates sub-Antarctic conditions during the Late-glacial. This was followed by the rapid transition to Holocene warmth at c. 10 ka and a significant period of aridity and increased fire frequency. Evidence for Antarctic Cold Reversal / Younger Dryas responses in the biological proxies is assessed. ON THE UTILITY OF INTEGRATING SOIL STRATIGRAPHY WITH RADIOMETRIC DATING IN THE STUDY OF ACTIVE FAULTS IN DESERT REGIONS: AN EXAMPLE FROM EASTERN CALIFORNIA, U.S.A Eric McDonald. Desert Research Institute, United States E-mail address: [email protected]
Alluvial fans comprise the principal Quaternary tectonic record in desert regions. The three most common methods used to date alluvial fans– radiocarbon, luminescence, and terrestrial cosmogenic nuclides (TCN)– have particular disadvantages in arid regions that limit their precision and applicability. Moreover, the expense of obtaining ages often limits application to a single site along a given structure. Integration of radiometric dating with a calibrated soil chronosequence using profile development indices (PDI) can provide a reliable chronologic framework across a region of similar climate. Soil stratigraphy can be widely applied for a fraction of time and cost of numerical ages and provides independent stratigraphic verification of radiometric ages. Previous attempts to establish PDI methods were hampered by unreliable chronologies for calibration and by the subjectivity of some of the indices used. A soil chronofunction developed for recent work along active faults in eastern California illustrates this integrated approach. Our soil chronosequence utilizes dated surfaces (OSL, 14 C, 10Be, 36Cl) from Panamint Valley and the western Mojave Desert ranging in age from about 1 to 150 ka. Detailed, reproducible, morphologic descriptions of soil development from multiple sites provide data for PDI's, enhances subdivision of local fan stratigraphy, and additionally ascertains local surface history critical for interpreting TCN results. Statistical analysis indicates that a more robust chronofunction can be developed using just 2 or 3 soil morphologic parameters rather than the more common practice of using 8 to 10 parameters. Age estimates from the PDI-based chronofunction indicate (1) rapid and extensive late Holocene (w2-4 ka) displacement of range front faults along the Panamint Mountains and southern flank of the Slate Range (Garlock fault), and (2) clarifies ages of Pleistocene fans displaced at multiple locations (w9-12 ka and w30-80 ka). THE EVOLUTION OF THE NORTH AFRICAN DUST PLUME OVER THE PAST 15,000 YEARS: INSIGHTS FROM DUST FLUXES MEASURED ALONG A MERIDIONAL TRANSECT David McGee. Lamont-Doherty Earth Observatory of Columbia Unive, United States E-mail address: [email protected]
317
Records of eolian dust accumulation in marine sediments provide important continuous records of the onset and termination of the African Humid Period (AHP), a period of enhanced monsoon precipitation in North Africa from approximately 11,000 to 5,000 years ago. Existing records indicate dramatic decreases in North African dust emissions during the AHP, suggesting similarly large-scale changes in continental vegetation and aridity. The limited spatial extent of these records, as well as the lack of highresolution flux data, do not allow us to determine whether changes in dust emissions occurred with similar timing, magnitude and abruptness throughout northwest Africa. Here we present new records from a meridional transect of cores stretching from 27 N to 19 S along the northwest African margin. By combining grain size endmember modeling with 230Thnormalized fluxes in these cores, we are able to document spatial and temporal changes in dust loads and grain size distributions within the North African dust plume throughout the last 15,000 years. Our results provide new insights into patterns of regional aridity and atmospheric circulation over this period. Additionally, they represent a robust target for models of past dust emissions and vegetation-climate feedbacks in the region. ABSOLUTE-DATED, HIGH-RESOLUTION RECORDS OF WATER BALANCE CHANGES DURING THE LAST GLACIAL PERIOD AND DEGLACIATION FROM LACUSTRINE CAVE DEPOSITS IN THE BONNEVILLE BASIN, UTAH, USA David McGee. Lamont-Doherty Earth Observatory of Columbia Unive, United States E-mail address: [email protected]
Closed-basin lakes within the semi-arid U.S. Great Basin expanded dramatically during the last glacial period, with Lake Bonneville, the largest of these lakes, covering an area of more than 50,000 km2. This change in water balance has been linked to a southward shift in the westerly storm track. Existing records from the Great Basin lack the dating precision and sample resolution to allow us to accurately determine the timing and rate of past lake level changes, however, limiting our understanding of the region's response to millennial-scale changes in Northern Hemisphere climate during the last glacial period and deglaciation. Here we present records from a novel paleohydrological archive from the northeastern Great Basin: carbonates precipitated within caves flooded by Lake Bonneville. Importantly, the deposits can be precisely dated by U-Th methods, providing the first high-precision, absolute-dated records of Lake Bonneville's water balance changes. The deposits appear to reflect periods when a) the lake was above a given cave's elevation and b) the lake was not overflowing and therefore exceeded calcite/aragonite saturation. Our data from multiple caves indicate that these deposits reflect the chemistry and isotopic composition of the lake rather than local effects. The deposits record the timing of the lake's passage through each cave's elevation and the onset and cessation of basin overflow between 26 and 13 ka, providing precise constraints on past lake level changes. High-resolution oxygen isotope records from the deposits suggest that the lake received a large influx of freshwater during Heinrich Event 2, while dates for the final stages of deposition indicate that the lake's deglacial regression began by as much as 1 kyr before the Bølling-Allerød warming. Future sampling of more caves from different elevations should provide further insights into changes in lake chemistry, isotopic composition and level. FACIES AND DEPOSITS ON STAGNATING GLACIAL ICE, GLACIAL LAKE PROVEN BASIN, RIDING MOUNTAIN UPLANDS, MANITOBA, CANADA Roderick McGinn. Brandon University, Canada E-mail address: [email protected]
The Glacial Lake Proven basin covers an area of approximately 340 km2 on the Riding Mountain Uplands in Manitoba, Canada. This paper reviews the sedimentary facies exposed in stratigraphic sections, sand and gravel extraction pits, shallow borrow pits and from a “GeoProbe” coring project in the Glacial Lake Proven basin. Glacial Lake Proven began as a shallow supraglacial “river lake” formed in a transition zone between stagnating ice on the Eastern Riding Mountain Uplands and the Assiniboine Lobe to the southwest. The eastern ridge of the “Horod Moraine” was deposited at the northwestern extension of this
HIGH RESOLUTION PALAEOCLIMATE LAKE AND PEAT RECORDS FROM FUEGO-PATAGONIA FROM THE LGM TO THE EARLY-HOLOCENE Robert McCulloch. University of Stirling, United Kingdom E-mail address: [email protected]
The southern Andes lie athwart the zone of westerly precipitation which sustains the maritime Patagonian ice fields. During the Last Glacial Maximum (LGM) the southern Andean ice fields formed a single coterminous ice cap, some 200 km wide and over 1,800 km long. Climate records from Fuego-Patagonia spanning the LGM and deglaciation are few. Palaeoclimate change has to date been inferred largely from reconstructions of glacial fluctuations of the outlet glaciers draining the ice fields. We present two high resolution palaeoecological records dated to 30.3 ka and 22.8 ka supported by sedimentological and geochemical proxies from Lago Pato, Torres del Paine (51oS) and Punta Yartou (53oS), Tierra del Fuego, southern Patagonia. Robust age-depth models are provided by 14C dating and tephra layers. These two records lie close to the present southern Beech forest / steppe zone of transition and provide sensitive records of shifts in these ecotonal boundaries in response to climatic variations. A synthesis of the two records demonstrates the early deglaciation of FuegoPatagonia following the LGM but the persistence of tundra vegetation indicates sub-Antarctic conditions during the Late-glacial. This was followed by the rapid transition to Holocene warmth at c. 10 ka and a significant period of aridity and increased fire frequency. Evidence for Antarctic Cold Reversal / Younger Dryas responses in the biological proxies is assessed. ON THE UTILITY OF INTEGRATING SOIL STRATIGRAPHY WITH RADIOMETRIC DATING IN THE STUDY OF ACTIVE FAULTS IN DESERT REGIONS: AN EXAMPLE FROM EASTERN CALIFORNIA, U.S.A Eric McDonald. Desert Research Institute, United States E-mail address: [email protected]
Alluvial fans comprise the principal Quaternary tectonic record in desert regions. The three most common methods used to date alluvial fans– radiocarbon, luminescence, and terrestrial cosmogenic nuclides (TCN)– have particular disadvantages in arid regions that limit their precision and applicability. Moreover, the expense of obtaining ages often limits application to a single site along a given structure. Integration of radiometric dating with a calibrated soil chronosequence using profile development indices (PDI) can provide a reliable chronologic framework across a region of similar climate. Soil stratigraphy can be widely applied for a fraction of time and cost of numerical ages and provides independent stratigraphic verification of radiometric ages. Previous attempts to establish PDI methods were hampered by unreliable chronologies for calibration and by the subjectivity of some of the indices used. A soil chronofunction developed for recent work along active faults in eastern California illustrates this integrated approach. Our soil chronosequence utilizes dated surfaces (OSL, 14 C, 10Be, 36Cl) from Panamint Valley and the western Mojave Desert ranging in age from about 1 to 150 ka. Detailed, reproducible, morphologic descriptions of soil development from multiple sites provide data for PDI's, enhances subdivision of local fan stratigraphy, and additionally ascertains local surface history critical for interpreting TCN results. Statistical analysis indicates that a more robust chronofunction can be developed using just 2 or 3 soil morphologic parameters rather than the more common practice of using 8 to 10 parameters. Age estimates from the PDI-based chronofunction indicate (1) rapid and extensive late Holocene (w2-4 ka) displacement of range front faults along the Panamint Mountains and southern flank of the Slate Range (Garlock fault), and (2) clarifies ages of Pleistocene fans displaced at multiple locations (w9-12 ka and w30-80 ka). THE EVOLUTION OF THE NORTH AFRICAN DUST PLUME OVER THE PAST 15,000 YEARS: INSIGHTS FROM DUST FLUXES MEASURED ALONG A MERIDIONAL TRANSECT David McGee. Lamont-Doherty Earth Observatory of Columbia Unive, United States E-mail address: [email protected]
317
Records of eolian dust accumulation in marine sediments provide important continuous records of the onset and termination of the African Humid Period (AHP), a period of enhanced monsoon precipitation in North Africa from approximately 11,000 to 5,000 years ago. Existing records indicate dramatic decreases in North African dust emissions during the AHP, suggesting similarly large-scale changes in continental vegetation and aridity. The limited spatial extent of these records, as well as the lack of highresolution flux data, do not allow us to determine whether changes in dust emissions occurred with similar timing, magnitude and abruptness throughout northwest Africa. Here we present new records from a meridional transect of cores stretching from 27 N to 19 S along the northwest African margin. By combining grain size endmember modeling with 230Thnormalized fluxes in these cores, we are able to document spatial and temporal changes in dust loads and grain size distributions within the North African dust plume throughout the last 15,000 years. Our results provide new insights into patterns of regional aridity and atmospheric circulation over this period. Additionally, they represent a robust target for models of past dust emissions and vegetation-climate feedbacks in the region. ABSOLUTE-DATED, HIGH-RESOLUTION RECORDS OF WATER BALANCE CHANGES DURING THE LAST GLACIAL PERIOD AND DEGLACIATION FROM LACUSTRINE CAVE DEPOSITS IN THE BONNEVILLE BASIN, UTAH, USA David McGee. Lamont-Doherty Earth Observatory of Columbia Unive, United States E-mail address: [email protected]
Closed-basin lakes within the semi-arid U.S. Great Basin expanded dramatically during the last glacial period, with Lake Bonneville, the largest of these lakes, covering an area of more than 50,000 km2. This change in water balance has been linked to a southward shift in the westerly storm track. Existing records from the Great Basin lack the dating precision and sample resolution to allow us to accurately determine the timing and rate of past lake level changes, however, limiting our understanding of the region's response to millennial-scale changes in Northern Hemisphere climate during the last glacial period and deglaciation. Here we present records from a novel paleohydrological archive from the northeastern Great Basin: carbonates precipitated within caves flooded by Lake Bonneville. Importantly, the deposits can be precisely dated by U-Th methods, providing the first high-precision, absolute-dated records of Lake Bonneville's water balance changes. The deposits appear to reflect periods when a) the lake was above a given cave's elevation and b) the lake was not overflowing and therefore exceeded calcite/aragonite saturation. Our data from multiple caves indicate that these deposits reflect the chemistry and isotopic composition of the lake rather than local effects. The deposits record the timing of the lake's passage through each cave's elevation and the onset and cessation of basin overflow between 26 and 13 ka, providing precise constraints on past lake level changes. High-resolution oxygen isotope records from the deposits suggest that the lake received a large influx of freshwater during Heinrich Event 2, while dates for the final stages of deposition indicate that the lake's deglacial regression began by as much as 1 kyr before the Bølling-Allerød warming. Future sampling of more caves from different elevations should provide further insights into changes in lake chemistry, isotopic composition and level. FACIES AND DEPOSITS ON STAGNATING GLACIAL ICE, GLACIAL LAKE PROVEN BASIN, RIDING MOUNTAIN UPLANDS, MANITOBA, CANADA Roderick McGinn. Brandon University, Canada E-mail address: [email protected]
The Glacial Lake Proven basin covers an area of approximately 340 km2 on the Riding Mountain Uplands in Manitoba, Canada. This paper reviews the sedimentary facies exposed in stratigraphic sections, sand and gravel extraction pits, shallow borrow pits and from a “GeoProbe” coring project in the Glacial Lake Proven basin. Glacial Lake Proven began as a shallow supraglacial “river lake” formed in a transition zone between stagnating ice on the Eastern Riding Mountain Uplands and the Assiniboine Lobe to the southwest. The eastern ridge of the “Horod Moraine” was deposited at the northwestern extension of this